1. Field of the Invention
This invention relates to the field of alkylene glycol manufactured by catalytic hydration of alkylene oxide.
2. Description of the Prior Art
Prior art methods for hydrating alkylene oxides to the alkylene glycols include the direct hydration reaction without benefit of catalyst and the catalytic hydration of alkylene oxides using mineral acid catalysts. These mineral acid catalytic reactions are homogeneous thereby posing a problem for the commercial production of glycols since the catalyst is carried over into the product and must be separated. Present commercial processes use a noncatalytic hydration procedure which must use large ratios of water to alkylene oxide thereby presenting a problem of separation of the water from the finished product. This separation consumes large amounts of energy which recently has been the cause of much concern.
Recently, attempts have been made to discover a new catalyst for the hydration of alkylene oxides to the respective glycols. U.S. Pat. No. 4,160,116 describes such a method using quarternary phosphonium salts as catalyst. The prior art section of that patent describes the use of other catalysts, among them tetramethyl ammonium iodide and tetraethyl ammonium bromide, as disclosed in British Pat. No. 117,877. Other prior art catalytic processes using, for example, organic tertiary amines such as triethylamine and pyrridine are disclosed in German OLS No. 2,615,595.
A novel and highly effective catalyst for the hydration of alkylene oxides to the respective glycols has been discovered. This catalyst has advantages which include heterogeneity as well as the suppression of production of noxious dioxane.